1. Field
The presently disclosed subject matter relates to a multi-color image forming apparatus such as a color electro-photographic printer, a color laser beam printer and a color print machine, and, more particularly, to an apparatus for measuring a deposited toner amount in a multi-color image forming apparatus.
2. Description of the Related Art
Generally, a multi-color image forming apparatus reproduces a clear image in accordance with a full-color mode, a monochromatic color mode, or a black and white print mode. For this purpose, toner rectangles or patches having predetermined amounts of magenta toner, predetermined amounts of cyan toner, predetermined amounts of yellow toner and predetermined amounts of black toner are deposited in advance to a toner carrier or a transfer belt. Then, the predetermined amounts of deposited toner of the patches are measured by a deposited toner amount measuring apparatus to thereby fine-adjust the charging process, the exposing process, the developing process, the transferring process, the fixing process and the like.
A prior art deposited toner amount measuring apparatus detects light reflected from a toner patch on a transfer belt irradiated with light, and measures a thickness of deposited toner in accordance with the difference between the height of the transfer belt at edges of the toner patch and the height of the toner patch. Thus, a thickness of deposited toner as the deposited toner amount can be measured regardless of a wavelike movement, roughness and fluttering of the transfer belt (see: JP2010-152138A).
In the above-described prior art deposited toner amount measuring apparatus, however, only a large amount of deposited toner can be measured, which is discussed below.
That is, in a thickness determining region TDR where a toner patch TP1 has a deposited toner amount W not smaller than 0.6 mg/cm2, for example, as illustrated in FIG. 21, the transfer belt (toner carrier) beneath the toner patch TP1 is entirely covered by toner particles thereof, so that the thickness “t” of deposited toner at the toner patch TP1 is proportional to the deposited toner amount W at the toner patch TP1 as illustrated in FIG. 23. Note that the deposited toner thickness “t” is increased at inner portions having a width of about 1 to 1.5 mm from the edges of the toner patch TP1, to improve the accuracy of the deposited toner thickness “t” by measuring them at such inner portions.
On the other hand, in an area determining region ADR where a toner patch TP2 has a deposited toner amount W smaller than 0.6 mg/cm2, for example, as illustrated in FIG. 22, the transfer belt (toner carrier) beneath the toner patch TP2 is not entirely covered by toner particles thereof, so that the thickness “t” of deposited toner at the toner patch TP2 is constant regardless of the deposited toner amount W at the toner patch TP2 as illustrated in FIG. 23.
In FIGS. 21 and 22, note that LR designates a reflection reference level at the transfer belt.
Thus, the above-described prior art deposited toner amount measuring apparatus measures only deposited toner amounts W in the thickness determining region TDR (W≧0.6 mg/cm2); however, the above-described prior art deposited toner amount measuring apparatus would not measure deposited toner amount W in the area determining region ADR (W<0.6 mg/cm2). If it is required to measure deposited toner amount W in the area determining region ADR, an additional deposited toner amount measuring apparatus is required, which would increase the manufacturing cost.
Additionally, the above-described prior art deposited toner amount measuring apparatus requires a line sensor and a specific optical system, which also would increase the manufacturing cost.